FOULING DEPOSITS ON A PILLOW PLATE HEAT EXCHANGER USED IN A SEWAGE SOURCE HEAT PUMP

Heat recovery from urban sewage represents an energy-efficient technology that significantly contributes to reducing carbon dioxide emissions. However, a major challenge in this process is the deposition of fouling on the surface of sewage heat exchangers, which can lead to a rapid decline in heat transfer performance. To address this issue, a pillow plate heat exchanger (PPHX) was developed to enhance the heat transfer efficiency while inhibiting fouling growth on the surface. Experimental results demonstrated that the PPHX could achieve a heat transfer performance of up to 1323.95 W/m<sup>2</sup>. The fouling induction period of the PPHX was 43 days, significantly longer than that of similar sewage heat exchangers (7-13 days), indicating superior anti-fouling performance. Simulation analysis revealed that increasing the longitudinal distance of the solder joints reduced the deposition rate, thereby mitigating fouling accumulation. Furthermore, the asymptotic fouling resistance was found to increase with higher particle concentrations, lower flow velocities, and smaller particle sizes. An increase in flow velocity significantly reduced the sticking probability while exerting only a minor influence on deposit bond strength. For applications of the proposed PPHX in sewage source heat pump systems, this study developed correlations for the sticking probability and deposit bond strength, two critical parameters affecting the fouling deposition process. By monitoring and analyzing fouling growth, the findings of this study provide valuable insights to facilitate practical engineering applications of the PPHX.